The hydrometallurgical processing of metal value containing ores or concentrates, typically comprises leaching with either an acidic or alkaline solution to produce a pregnant leach solution, from which the metal values are extracted. Depending on the chemical nature of the metal values, one means of recovering them from solution is by precipitation as metal sulfides. Examples of metals that can be recovered by precipitation as metal sulfides include nickel, cobalt, zinc, copper, gold, silver, iron, gallium, germanium, arsenic, cadmium, indium, tin, antimony, platinum, palladium, mercury, thallium, lead and bismuth.
However, sulfide precipitation as a recovery mechanism can be problematic where the metal sulfides are prone to slimes formation. Slimes refers to the precipitation of very fine particles of metal sulfides (typically, less than 0.0635 mm in diameter, or less than mesh number 200) which can be very difficult to separate from solution by conventional means such as by using thickeners, filters or counter current decantation. In the case of thickeners this is due to the difficulty in achieving adequate settling density of the very fine particles, and also the desire to avoid carryover of particles into the overflow, whereas in the case of filters the fine particles can “blind” the filtration media, or pass completely through it.
There is accordingly a need for a process for increasing the density of metal sulfides from a product leach solution, which thereby minimises the formation of slimes.
References to prior art in this specification are provided for illustrative purposes only and are not to be taken as an admission that such prior art is part of the common general knowledge in Australia or elsewhere.